The prior-art switching power supply controller is a controller primarily using the normal rate and variable frequency for the control as shown in FIG. 6. The charge and discharge of electricity of each oscillated circuit are set by means of connecting the resistor to the RT terminal, of which the RT terminal is connected to the FB terminal through the resistor to provide (controlled by light) a control frequency. CT1 is connected to the output terminal of the oscillated circuit of a capacitor, and capable of generating a trigonometric wave oscillation between the lower limit LL and the upper limit UL by means of the current at RT terminal. CT2 is connected to the terminal of a capacitor to generate and provide a serrated wave to enable 1/20 of the current at the CR1 terminal to pass and produce serrated wave oscillations between the lower limit and upper limit. However, the method described above is not necessarily a good method for certain power transfer elements, particularly to those power transfer elements having the property of a bandpass filter; a change of the input frequency may result in a change of output voltage, but a great deal of input power is absorbed by such power transfer elements. Therefore a long time use may break down such elements or expedite their aging, and thus affecting the reliability of the whole system.
Furthermore, if the output end requires a dimming, a burst timing circuit is generally used to intermittently transfer the output power (as shown in FIGS. 7-1 to 7-3), and the power transfer element varies the power or voltage and sends the power to the loading element. However, such method has a substantial shortcoming, because the intermittent ON/OFF will transiently impact the power transfer element (from zero power to maximum power) and will also cause such element to produce audible noise.